The Archbishop of Canterbury has waded into the row over energy prices, warning that the latest wave of hikes looks "inexplicable".

Justin Welby insisted the Big Six companies had an obligation to behave morally rather than just maximising profit.

The intervention, in an interview with the Mail on Sunday, came after British Gas followed in the footsteps of SSE by announcing a 9.2% increase in prices.

The head of the Church of England, himself a former oil executive, said he understood the anger the rises were generating.

"The impact on people, particularly on low incomes, is going to be really severe in this, and the companies have to justify fully what they are doing," Mr Welby said.

"I do understand when people feel that this is inexplicable, and I can understand people being angry about it, because having spent years on a low income as a clergyman I know what it is like when your household budget is blown apart by a significant extra fuel bill and your anxiety levels become very high. That is the reality of it."

The Archbishop urged firms to be "conscious of their social obligations", saying they had to to "behave with generosity and not merely to maximise opportunity".

"They have control because they sell something everyone has to buy. We have no choice about buying it," he said. 'With that amount of power comes huge responsibility to serve society.

"It is not like some other sectors of business where people can walk away from you if they don't want to buy your product and you are entitled to seek to maximise your profit.

"The social licence to operate of the energy companies is something they have to take very, very seriously indeed."

Mr Welby said he was concerned that fuel poverty was "a very severe issue... because real incomes are flat or declining and the cost of energy has gone up".

"It ties in with the food banks and the debt. They are all part of the reality of life for many people today," he added.

The comments came amid a bitter political spat over energy which has seen Ed Miliband attempt to seize the initiative by pledging a 20 month price freeze.

David Cameron has dismissed the idea as a "con", and encouraged consumers to switch suppliers to keep bills down.

But polls have suggested that Labour's promise is popular with voters, putting pressure on the coalition to respond.

According to the Sun on Sunday, Sir Roger Carr - chairman of Centrica, which owns British Gas - is serving on the Prime Minister's Business Advisory Group.

Deputy Prime Minister Nick Clegg said it was not clear why power companies needed to hike bills.

He said Energy Secretary Ed Davey had written to them demanding more transparency over their costs and profits.

"Clearly the companies need to justify the bill increases that they are now announcing," the Liberal Democrat leader told Sky News' Murnaghan programme.

"It cannot be right that people who are really struggling - many, many people still struggling to pay their weekly, their monthly bills, where electricity and gas bills for this winter are a looming worry - it can't be right that those bills are increased for those households in our country and yet it is all rather opaque about what drives these increases.

"Because some of the companies are not really open enough yet and transparent enough yet about their own balance sheet."

He added: "We do need not only more competition so people can switch to lower tariffs where possible - we are legislating automatically to put people on the lowest available tariff - but also to get transparency in the way these companies account for themselves.

"Not only to their shareholders, but to the public."

Mr Clegg shrugged off questions about why the chairman of Centrica was advising the Prime Minister.

"I don't think we can just slam the door in the face of the people who work in these companies," he said.